This invention relates to vehicle leveling systems of the type which automatically respond to one or more level sensors to maintain a predetermined level of the sprung mass of the vehicle relative to the unsprung road wheels as the loads on various portions of the vehicle change.
Although such vehicle leveling systems have been known for some time and the prior art is crowded with devices and controls, there has been little attention paid to the side to side leveling of the vehicle under static conditions. Such leveling is controllable by systems of the three or four corner variety, wherein at one or both ends of the vehicle the levels of the sides are independently adjustable.
Side to side leveling is important primarily for appearance purposes. Most vehicles have a shorter distance from side to side between wheels than from front axle to rear axle. Thus, differences in level from side to side produce a slightly greater slant in the vehicle body relative to the ground than the same differences from front to rear. In addition, the shape of most vehicles when viewed from the front or back, and especially the low, straight bumper line, appears to accentuate slight differences in level between the sides of the vehicle that would not be apparent in front to back level when viewed from the side of the vehicle. Finally, people are more inclined to accept differences in level between front and rear as opposed to such differences from side to side, since the former may be viewed as a positive design feature such as a "rake" for streamlining while the latter is generally not so construed. Therefore, even though there is actually nothing wrong with a vehicle that may have an inch or so difference in side to side level, it is desirable to reduce this difference when possible to produce a quality appearance for customer satisfaction. This calls for a leveling system with more accuracy than prior art systems have shown.
On the other hand, it is not desirable for the level system to be continually cycling as it responds to every tiny difference in level at each corner. The sound of the compressor and other fluid components can be annoying, especially when the vehicle is stationary so that there is no masking of the sound by other, more expected sounds. To avoid this, leveling systems generally use dead bands and/or hysteresis in responding to the height sensor signals. Once again, the issue is customer satisfaction; and the two somewhat conflicting concerns must be reconciled.